A fine granular substance produced in flowers. Technically a collective term for pollen grains (microspores) produced in the anthers of flowering plants. (This specific usage dating from mid 18th century.)

Fine powder in general, fine flour. (16th-century usage documented by the OED.)

“"...and ther was good wyne of Gascoyne,... as well of pollen, as of other vitailes..." Froissart, Jean, 1338?-1410?; Berners, John Bourchier, Lord https//archive.org/details/chroniclefroiss00froigoog”

To cover with, or as if with, pollen.